For all intents and purposes, Valve's Orange Box - a game combo that included Half-Life 2, its two subsequent episodes, Team Fortress 2, and Portal - was supposed to be more of a packaging showcase rather than putting any single entry on a gaming pedestal. It was meant as a consumer-oriented value proposition led by the strength of the Half-Life brand and tapping into nostalgia for the classic Team Fortress. Yet, it was the little-title-that-could - Portal, that garnered the most critical attention.

Developed by a group of students at the DigiPen Institute of Technology, Portal went from under-the-radar to Orange Box centerpiece. Instead of people reserving it as the last stop on their Orange Box tour, they made it their first. 2007 became the year of Portal in-jokes on message boards and among gamers. It seemed like people were always mentioning the "cake is a lie" and waxing poetic about the heart-shaped Companion Cube.

Portal: Still Alive strips the original Portal from the Orange Box, allowing it to bask in its own dedicated glow. New to this downloadable version (available at 1,200 MS Points) are stat tracking features and 14 levels from Portal: The Flash Version originally developed by the group We Create Stuff. If you missed Portal the first time around, this is the version to get and for those that already have the Orange Box, it provides plenty of new challenges to justify the price tag.

Students of behaviorism should be familiar with the operant conditioning box (also known by the name Skinner Box on account of its creator, B.F. Skinner). You place an organism in an enclosed area, blocking stimuli from the outside (like light and sound), so that only selected forms of stimuli can be directed at the quarantined subject. There's usually some kind of incentive to keep the subject reacting - the most common example is a rat rewarded with pellets from a feeder. Portal takes this bit of psychology and twists it to its own end: you're the rat, stuck in a series of Skinner Boxes and instead of pellets, there's the promise of cake, plus grief counseling (the first note of the game's sense of humor).

The deliverer of this promise is GLaDOS (voiced by Ellen McLain), the A.I. that watches over Aperture Science, a direct competitor to Gordon Freeman's employer: Black Mesa. One chamber at-a-time, GlaDOS slowly lays out the rules of the world. It's all handled in a very well-paced manner. You're first taught about the nature of portals - teleporting pockets that allow you to traverse from one area to another - and then given a gun that allows you to create your own. By shooting an orange portal, you set up a point of departure, and once a blue portal is laid down, you have an exit. One-by-one, more elements are introduced. You learn to use weighted cubes to hold down switches and how to direct energy orbs into receptacles to unlock doors.

Again, it's the way that Portal handles introducing all these elements that makes it so successful. Even though the laws of physics are being bent, at no point is it hard to wrap your mind around the concepts on display. When you first learn that you can use momentum to rocket yourself from one portal to another, a light bulb goes off, making you say, "Why didn't I think of that already?" True to her tongue-in-cheek nature, GlaDOS lays out the process, saying, "Momentum: A function of mass and velocity conserved between portals. In layman's terms, speedy thing goes in, speedy thing comes out."

Yet all is not well - a slightly sinister tinge is added to the way GLaDOS delivers her lines as the games progresses. It's not just the dialogue: you'll notice that the while the objectives are the same (escape each test chamber), the obstacles are more deadly. What were once safe pits, composed of tiles, are later filled with acid; hallways are marked by sentry turrets; and giant mechanical compressors will raise you up one moment, only to try and squash you the next. This sudden increase in environmental danger is compounded by cryptic signs left by previous test chamber subjects: such as bloody hand prints and demented scribblings etched into walls just off the beaten path.